When Korach and two hundred and fifty people came to complain to Moshe with regard to Bnei Yisroel's leadership, Moshe proceeded to prove that the leaders were appointed directly by Hashem. He told each of the two hundred and fifty complainers to offer incense as a means of determining the true leader. Hashem's acceptance of one person's incense would be the indicator as to whom He had chosen to be the leader.
The Torah tells us that Moshe davened to Hashem that He not accept their offerings. "And he said to Hashem do not turn to their offerings; not even one donkey did I take from them, nor did I harm any of them" (Bamidbar 16, 15). Rashi explains that when Moshe traveled from Midyan to Mitzrayim to redeem Bnei Yisroel, he rode on his own donkey rather than take one from Bnei Yisroel.
Rav Wolbe asks (Shiurei Chumash) what would have been so terrible if he did take a donkey to transport his family from Midyan? Didn't he deserve to have his transportation sponsored by those he came to redeem and the flock he would tend? The answer is that Moshe was declaring that he was free from any negi'os (bias) in his role as Bnei Yisroel's leader because he did not earn any money in this position. He could have declared that for their sake he put his life on the line or that he sacrificed immeasurable amounts of time and effort. However, the true test to gauge one's greatness is in the area of money matters. If one does not maintain a clean slate in this area, then he could not present an argument in his favor. Moshe was claiming that in his position as a leader he didn't even take travel expenses, and was therefore worthy of Hashem's backing.
Likewise, we find that when Moshe accepted the donations for the Mishkan, he wore clothing that had no pockets or seams, lest Bnei Yisroel think - even for a second - that he had taken some of the money for himself. His scrupulousness in money matters was so great that he didn't allow even a doubt to creep into anyone's mind that he had taken some of the money allocated for the Mishkan.
There is no way to live without money. However, we must be sure that our money is earned honestly, for integrity in the area of money is one of the defining factors of how great we really are.